1. Field of the Invention
This invention relates to an attendant console sharing system in a centrex, and particularly control of an attendant console sharing system in a centrex.
More specifically, the present invention relates to improvements in operability of an attendant console and to flexibility of an extension line numbering plan for business groups in a case wherein the attendant console is shared by a plurality of business groups such as a plurality of enterprises located in the same premises for purposes of economy.
2. Description of the Related Art
FIG. 1 is a view showing an example of a conventional centrex system.
Attendant console 21c is provided for a specific business group such as business group C, and performs call connection assistance to extension line stations 81c and 82c and their counterpart in communication through central office 1A.
However, in order to reduce the economic burden of installing an attendant console, it is required to share an attendant console among centrex customers. Based on the centrex service, business groups D and E join in a group forming a centrex complex 13 and share attendant console 22. In this instance, when a call to a pilot number of one of business groups D or E arrives, the call is connected to attendant console 22, and assistance to call connection to one of extension line stations 81d to 83d in business group D or extension line stations 81e to 83e in business group E is performed by attendant console 22. In this instance, if some extension line numbers overlap among the business groups which share the attendant console, since an extension line station cannot be designated from the attendant console, an extension line number allocation condition (numbering plan) must be decided among the business groups.
In the example of FIG. 1, extension line numbers of the one hundred level such as 111, 112 and 113 are allocated to extension line stations 81d to 83d of business group D, respectively, and extension line numbers of the two hundred level such as 211, 212 and 213 are allocated to extension line subscribers 81e to 83e of business group E, respectively.
FIG. 7 is a diagrammatic view showing an example of an attendant console sharing system with a conventional private branch exchange (for example, Japanese Patent 62-239757/1987). In the second conventional system shown in FIG. 7, business groups F and G share private branch exchange 14, and business group numbers nf and ng are allocated to extension line stations such as 81f and 82f and extension line stations 81g and 82g belonging to business groups F and G, respectively. Separately, central office trunks 151f and 152f and central office trunks 151g and 152g, which interconnect private branch exchange 14 and central office 1B, have business group numbers nf and ng allocated thereto corresponding to business groups F and G to which they belong, respectively.
Attendant consoles 21 and 22 are shared by business groups F and G. Means for connecting 16, via switching unit 160, discriminates between intra-business group number nf or ng to which an incoming call from an extension line station or a tie trunk belongs and connects the call to attendant console 21 or 22. Consequently, attendant console 21 or 22 enters into the same condition as belonging exclusively to business group F or G and can perform connection assistance to the business group for which the call is destined.
The attendant console sharing system of the conventional examples described above, however, are individually disadvantageous in the following points. In particular, the first conventional system shown in FIG. 1 is disadvantageous in that a numbering plan for allocation of extension line numbers must be decided in advance so that extension line numbers do not overlap among business groups which share the attendant console, resulting in service which is inferior in flexibility and convenience to users.
Further, the first conventional system shown in FIG. 1 does not have a countermeasure against the situation that, when the attendant console accepts an incoming call to a business group and then tries to call a called extension line station and to connect the incoming call to the called extension line station, it calls a separate wrong extension line station in another business group in the same centrex complex and connects the incoming call to the thus-called extension line station in error. For example, referring to FIG. 1, when a call dialed to a pilot number of business group D arrives at attendant console 22 and connection to extension line station 81d of business group D is requested, if extension line number 111 is dialed as 211 in error, the call is connected to extension line station 81e of business group E. However, since no countermeasure against erroneous connection is taken in this instance, there is the possibility that a problem of security may arise.
The second conventional system adopted by the private branch exchange shown in FIG. 7 as another example of a conventional attendant console sharing system employs the method wherein a business group is discriminated from a trunk number since a group of tie trunks between the private branch exchange and the central office is allocated for each business group. However, in the centrex to which take present invention is directed, a call may possibly come from unspecified public network subscriber 91 or 92 or through one of tie trunks 10 which are not specified for business group F or G as shown in FIG. 2. Accordingly, a private branch exchange system cannot be adopted.